The present invention relates generally to porous materials having high surface areas, and more particularly to such materials which are degradable or partially degradable, and methods for fabricating the same.
Membranes have been typically used for filtration (microfiltration, ultrafiltration, nanofiltration), reverse osmosis (hyperfiltration), dialysis, pervaporation, and gas separation applications. See, for example, Scott, K. and R. Hughes, Industrial Membrane Separation Technology, 1996, London: Blackie Academic & Professional; Baker, R. W., Membrane technology and applications, McGraw-Hill professional engineering, 2000, New York: McGraw-Hill; and Cardew, P. T., M. S. Le, and Royal Society of Chemistry, Process Technology Group, Membrane processes: a technology guide, 1998, Cambridge: Royal Society of Chemistry.
A solid membrane can be made of synthetic polymers, natural macromolecules, inorganic compounds, ceramic or metallic materials. These membrane materials are generally fabricated through sintering, stretching, extrusion, phase inversion and etching, or casting. See, for example, Scott, K. and R. Hughes, Industrial Membrane Separation Technology, 1996, London: Blackie Academic & Professional; and Pinnau, I. and B. D. Freeman, Membrane formation and modification, ACS symposium series, 744, 2000, Washington, D.C. [New York]: American Chemical Society, Distributed by Oxford University Press.
Porous membranes are advantageous in their low resistance to mass transfer of solutes in solution due to the increased permeation rate resulting from the pores. Therefore, porous membranes have been employed for separation of mixtures of proteins and macromolecules, salt concentration, sterilization, etc. They can also serve as 3-D matrices for chemical and biochemical mass exchange or reactions to take place, or for cells or other living organisms (e.g., bacteria, viruses, fungi) to grow. Therefore, they can be used as matrices in diagnostic systems, catalysis systems, culture systems, drug delivery systems, wound dressings, etc.
U.S. Pat. No. 6,146,892 discloses a method for producing nanofibrillar matrices utilizing degradable polymers, such as for example, poly(L-lactic acid) (PLLA), poly(D,L-lactic acid-co-glycolic acid) (PLGA), and the like. The disclosed nanofibrillar matrices are highly porous and work well for various applications. However, the pores sizes are very small (on the order of 2 μm to 3 μm), which may in some instances render it more difficult for cells to enter. Further, small pore sizes may render it more difficult for material transport, especially materials which are particulate or contain particles. Yet further, the disclosed non-fibrillar structure (a platelet structure) was not as mechanically strong as may be desirable in some instances.